Ballygalley is just around the corner from Drains Bay in the previous post, separated by a rocky promontory. There is an extensive boulder lag (basalt, I think) between the slipway (boat ramp) at the east end of the bay and the beach in Ballygalley itself.
The beach at Ballygalley is a broad pocket of sand and gravel, maintained by the orientation of the coastline, and backed by a combination of cobble berms and seawalls.
Given my short visit, my limited observations, and my lack of thorough homework, most of my geological interpretations are little more than speculation. The Antrim Plateau, which reaches the coast itself in places, is capped with basalt, dating to extensive volcanism 60-80 million years ago. It is underlain by a wide variety of Paleozoic and Mesozoic sedimentary and metamorphic rocks, some of which - chalks and clays, for example - are prone to landslides that can bring down the basaltic cap rock. The Antrim coast is marked by many large slides that extend from divots in the edge of the plateau down to the coast. These can be seen in the aerial imagery and, at least to my eye, looks like what may have formed this boulder-strewn shore.